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Search found 882 results on 36 pages for 'concurrency coordination'.

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  • The architecture and technologies to use for a secure, fast, reliable and easily scalable web application

    - by DSoul
    ^ For actual questions, skip to the lists down below I understand, that his is a vague topic, but please, before you turn the other way and disregard me, hear me out. I am currently doing research for a web application(I don't know if application is the correct word for it, but I will proceed w/ that for now), that one day might need to be everything mentioned in the title. I am bound by nothing. That means that every language, OS and framework is acceptable, but only if it proves it's usefulness. And if you are going to say, that scalability and speed depend on the code I write for this application, then I agree, but I am just trying to find something, that wouldn't stand in my way later on. I have done quite a bit reading on this subject, but I still don't have a clear picture, to what suits my needs, so I come to you, StackOverflow, to give me directions. I know you all must be wondering what I'm building, but I assure you, that it doesn't matter. I have heard of 12 factor app though, if you have any similar guidelines or what is, to suggest the please, go ahead. For the sake of keeping your answers as open as possible, I'm not gonna provide you my experience regarding anything written in this question. ^ Skippers, start here First off - the weights of the requirements are probably something like that (on a scale of 10): Security - 10 Speed - 5 Reliability (concurrency) - 7.5 Scalability - 10 Speed and concurrency are not a top priority, in the sense, that the program can be CPU intensive, and therefore slow, and only accept a not-that-high number of concurrent users, but both of these factors must be improvable by scaling the system Anyway, here are my questions: How many layers should the application have, so it would be future-proof and could best fulfill the aforementioned requirements? For now, what I have in mind is the most common version: Completely separated front end, that might be a web page or an MMI application or even both. Some middle-ware handling communication between the front and the back end. This is probably a server that communicates w/ the front end via HTTP. How the communication w/ the back end should be handled is probably dependent on the back end. The back end. Something that handles data through resources like DB and etc. and does various computations w/ the data. This, as the highest priority part of the software, must be easily spread to multiple computers later on and have no known security holes. I think ideally the middle-ware should send a request to a queue from where one of the back end processes takes this request, chops it up to smaller parts and buts these parts of the request back onto the same queue as the initial request, after what these parts will be then handled by other back end processes. Something *map-reduce*y, so to say. What frameworks, languages and etc. should these layers use? The technologies used here are not that important at this moment, you can ignore this part for now I've been pointed to node.js for this part. Do you guys know any better alternatives, or have any reasons why I should (not) use node.js for this particular job. I actually have no good idea, what to use for this job, there are too many options out there, so please direct me. This part (and the 2. one also, I think) depend a lot on the OS, so suggest any OSs alongside w/ the technologies/frameworks. Initially, all computers (or 1 for starters) hosting the back end are going to be virtual machines. Please do give suggestions to any part of the question, that you feel you have comprehensive knowledge and/or experience of. And also, point out if you feel that any part of the current set-up means an instant (or even distant) failure or if I missed a very important aspect to consider. I'm not looking for a definitive answer for how to achieve my goals, because there certainly isn't one, for I haven't provided you w/ all the required information. I'm just looking for recommendations and directions on what to look into. Also, bare in mind, that this isn't something that I have to get done quickly, to sell and let it be re-written by the new owner (which, I've been told for multiple times, is what I should aim for). I have all the time in the world and I really just want to learn doing something really high-end. Also, excuse me if my language isn't the best, I'm not a native. Anyway. Thanks in advance to anyone, who takes the time to help me out here. PS. When I do seem to come up w/ a good architecture/design for this project, I will certainly make it an open project and keep you guys up to date w/ it's development. As in what you could have told me earlier and etc. For obvious reasons the very same question got closed on SO, but could you guys still help me?.

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  • Adopt a Java EE 7 JSR!

    - by reza_rahman
    Broad community participation is key to the success of any technology worth it's salt. The Adopt-a-JSR program was launched in recognition of this fact. It is an initiative by some key JUG leaders around the World to encourage JUG members to get involved in a JSR and to evangelize that JSR to their JUG and the wider Java community, in order to increase grass roots participation. There are a number of JUGs that have already jumped in like the Chennai JUG, SouJava, London Java Community, BeJUG, GoJava, Morrocco JUG, Campinas JUG and ItpJava. Note that any developer can participate, there isn't a need to be a JUG leader. There are a number of Java EE 7 JSRs that could use your help right now including WebSocket, JSON, Caching, Concurrency for EE, JAX-RS2 and JMS2. Find out more here.

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  • Database Context and Singleton injection with IoC

    - by zaitsman
    All of the below relates to a ASP.NET c# app. I have a Singleton Settings MemoryCache that reads values from database on first access and caches these, then invalidates them using SQL Service Broker message and re-reads as required. For the purposes of standard controllers, i create my Db Context in a request scope. However, this obviously means that i can't use the same context in the Settings Cache class, since that is a singleton and we have a scope collision. At the moment, i ended up with two db contexts - the Controllers get it via IoC container, whereas a Singleton just creates it's own. However, i am not satisfied with this approach (mostly due to the way i feel about two contexts, the cache doesn't set anything on the db hence concurrency is not an issue as much). What is a better way to do it?

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  • Designing a hierarchical structure with lots of reads and writes?

    - by JD01
    I am in the process of working on a video on demand system part of it involves the management of a hierarchical tree structure (think windows explorer) which allows users to upload videos, move folders around, create new folders etc. User action will be allowed depending on which permissions they have. In addition to managing the structure (creating folders and uploading videos), subscribers will be viewing content (read access). The number of reads will be significantly more than the writes. My question (and it is big one) is should I store the data in a database (for the writes) and also have some sort of cache which will be used for the reads? or do I use two databases? or is there a better solution? Also I will have to resolve concurrency issues which I think optimistic locking on the database will resolve. I have a fair bit about CQRS over the last few months but not sure if this is the way to go. Any ideas?

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  • how to enrich my programming background? [on hold]

    - by city
    I am not sure whether I post my question in right place. I am a master student in computer science and I will graduate next year.Recently, I failed in an interview. Because (at least I think) the interviewer did not think my background strong enough although I finished 5 courses projects and currently working on other 2 projects in graduate school. It seems that nowadays, recruiters like these candidates who finish some projects out of school/work. So I wanna enrich my background. So, I hope you guys recommend some java/C++ projects to me, which I can finish in two or three months. And it would be better if concurrency programming or other fancy skills are needed.

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  • Tomcat threads vs Java threads

    - by black666
    When using java threads, one has to take care of the basic problems that come with concurrency through synchronization etc. AFAIK Tomcat also works with threads to handle its workload. Why is it, that I don't have to think about making my code threadsafe when it is running in Tomcat?

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  • Multiple NSOperationQueues?

    - by Infinity
    Hello! I would like to use NSOperations in my application to resolve threading problems. I have read some tutorials and now I know what I have to do, but I have a problem. There is a must to have the same NSOperationQueue in each class. What if I use a new NSOperationQueue in each class. There will be concurrency problems?

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  • Object database for website

    - by Damian
    I was planning to use db4o for a website. It's a microblog site with small posts and comments developed in java. The thing is I contacted db4o support asking if db4o would be suitable for a website, and they answered me that only for websites with low concurrency. That means with few requests? So, now I think db4o will not be a good choice. Do you know if there is any object database for java suitable for a website?

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  • How fast is Berkeley DB SQL compared to SQLite?

    - by dan04
    Oracle recently released a Berkeley DB back-end to SQLite. I happen to have a hundreds-of-megabytes SQLite database that could very well benefit from "improved performance, concurrency, scalability, and reliability", but Oracle's site appears to lack any measurements of the improvements. Has anyone here done some benchmarking?

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  • Help me choose between Go and Io

    - by Robert Smith
    During the following months I'll have some spare time so I thought of picking up a new programming language.I've been reading some articles about Go and Io and both of them look interesting and very promising so I'm stuck making a decision about which one to pick up next. I'm mainly interested in distributed systems and concurrency. Any help is greatly appreciated. Thanks.

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  • Why better isolation level means better performance in MS SQL Server

    - by Oleg Zhylin
    When measuring performance on my query I came up with a dependency between isolation level and elapsed time that was surprising to me READUNCOMMITTED - 409024 READCOMMITTED - 368021 REPEATABLEREAD - 358019 SERIALIZABLE - 348019 Left column is table hint, and the right column is elapsed time in microseconds (sys.dm_exec_query_stats.total_elapsed_time). Why better isolation level gives better performance? This is a development machine and no concurrency whatsoever happens. I would expect READUNCOMMITTED to be the fasted due to less locking overhead.

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  • BerkeleyDB vs. Tokyo Cabinet

    - by vsedach
    I'm looking for general experiences from people who have used both, particularly on how the two compare on handling large numbers of records, transaction/concurrency/deadlock handling, and juicy stories about database corruption and backup procedures.

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  • Redirecting multiple stdouts to single file

    - by obvio171
    I have a program running on multiple machines with NFS and I'd like to log all their outputs into a single file. Can I just run ./my_program >> filename on every machine or is there an issue with concurrency I should be aware of? Since I'm only appending, I don't think there would be a problem, but I'm just trying to make sure.

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  • Software Architecture: Unit of Work design pattern discussion

    - by santiagobasulto
    Hey everybody. According Martin Fowler's Unit of Work description: "Maintains a list of objects that are affected by a business transaction and coordinates the writing out of changes and resolution of concurrency problems." Avoiding very small calls to the database, which ends up being very slow I'm wondering. If we just delimit it to database transaction management, won't prepare statements help with this?

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  • Optimizing tasks to reduce CPU in a trading application

    - by Joel
    Hello, I have designed a trading application that handles customers stocks investment portfolio. I am using two datastore kinds: Stocks - Contains unique stock name and its daily percent change. UserTransactions - Contains information regarding a specific purchase of a stock made by a user : the value of the purchase along with a reference to Stock for the current purchase. db.Model python modules: class Stocks (db.Model): stockname = db.StringProperty(multiline=True) dailyPercentChange=db.FloatProperty(default=1.0) class UserTransactions (db.Model): buyer = db.UserProperty() value=db.FloatProperty() stockref = db.ReferenceProperty(Stocks) Once an hour I need to update the database: update the daily percent change in Stocks and then update the value of all entities in UserTransactions that refer to that stock. The following python module iterates over all the stocks, update the dailyPercentChange property, and invoke a task to go over all UserTransactions entities which refer to the stock and update their value: Stocks.py # Iterate over all stocks in datastore for stock in Stocks.all(): # update daily percent change in datastore db.run_in_transaction(updateStockTxn, stock.key()) # create a task to update all user transactions entities referring to this stock taskqueue.add(url='/task', params={'stock_key': str(stock.key(), 'value' : self.request.get ('some_val_for_stock') }) def updateStockTxn(stock_key): #fetch the stock again - necessary to avoid concurrency updates stock = db.get(stock_key) stock.dailyPercentChange= data.get('some_val_for_stock') # I get this value from outside ... some more calculations here ... stock.put() Task.py (/task) # Amount of transaction per task amountPerCall=10 stock=db.get(self.request.get("stock_key")) # Get all user transactions which point to current stock user_transaction_query=stock.usertransactions_set cursor=self.request.get("cursor") if cursor: user_transaction_query.with_cursor(cursor) # Spawn another task if more than 10 transactions are in datastore transactions = user_transaction_query.fetch(amountPerCall) if len(transactions)==amountPerCall: taskqueue.add(url='/task', params={'stock_key': str(stock.key(), 'value' : self.request.get ('some_val_for_stock'), 'cursor': user_transaction_query.cursor() }) # Iterate over all transaction pointing to stock and update their value for transaction in transactions: db.run_in_transaction(updateUserTransactionTxn, transaction.key()) def updateUserTransactionTxn(transaction_key): #fetch the transaction again - necessary to avoid concurrency updates transaction = db.get(transaction_key) transaction.value= transaction.value* self.request.get ('some_val_for_stock') db.put(transaction) The problem: Currently the system works great, but the problem is that it is not scaling well… I have around 100 Stocks with 300 User Transactions, and I run the update every hour. In the dashboard, I see that the task.py takes around 65% of the CPU (Stock.py takes around 20%-30%) and I am using almost all of the 6.5 free CPU hours given to me by app engine. I have no problem to enable billing and pay for additional CPU, but the problem is the scaling of the system… Using 6.5 CPU hours for 100 stocks is very poor. I was wondering, given the requirements of the system as mentioned above, if there is a better and more efficient implementation (or just a small change that can help with the current implemntation) than the one presented here. Thanks!! Joel

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  • mod_wsgi daemon mode vs threaded fastcgi

    - by t0ster
    Can someone explain the difference between apache mod_wsgi in daemon mode and django fastcgi in threaded mode. They both use threads for concurrency I think. Supposing that I'm using nginx as front end to apache mod_wsgi. UPDATE: I'm comparing django built in fastcgi(./manage.py method=threaded maxchildren=15) and mod_wsgi in 'daemon' mode(WSGIDaemonProcess example threads=15). They both use threads and acquire GIL, am I right?

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  • Will this SQL screw up

    - by Joshua
    I'm sure everyone knows the joys of concurrency when it comes to threading. Imagine the following scenario on every page-load on a noobily set up MySQL db: UPDATE stats SET visits = (visits+1) If a thousand users load the page at same time, will the count screw up? is this that table locking/row locking crap? Which one mysql use.

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  • If you could take one computer science course now, what would it be?

    - by HenryR
    If you had the opportunity to take one computer science course now, and as a result significantly increase your knowledge in a subject area, what would it be? Undergraduate or graduate level. Compilers? Distributed algorithms? Concurrency theory? Advanced operating systems? Let me know why. (Note that I appreciate this isn't a far fetched scenario - but time and inertia might be preventing people from taking the course or reading the book or whatever)

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  • A lightweight application framework for PHP?

    - by millenomi
    I have long been a fan of _why's Camping microframework -- lightweight, great for microscopic applications (low concurrency, easy to use and edit and maintain), which is what I do. I'd love to know if there's something similar for PHP; full-blown app frameworks like CakePHP or Symphony are very large for what I do, but I can't seem to find nothing "less". What PHP framework would you prefer, in this situation?

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  • How can I make a single WCF method ConcurrencyMode.Multiple when service is ConcurencyMode.Single

    - by Michael Hedgpeth
    I have a service which is defined as ConcurrencyMode.Single: [ServiceBehavior(ConcurrencyMode = ConcurrencyMode.Single, UseSynchronizationContext = false, InstanceContextMode = InstanceContextMode.PerSession, IncludeExceptionDetailInFaults = true)] public class MyService : IMyService This service provides a method to tell the client what it's currently working on: [OperationContract] string GetCurrentTaskDescription(); Is there a way to make this particular method allowable while another long-running task is running where all other methods still follow the single-threaded concurrency model?

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  • Two Phase Commit with MongoDB

    - by mattcodes
    Heres what Im thinking. Do you see any issues with this workaround to emulate 2 phase commit when using something like MongoDB where each operation is atomic and there is no support for transactions outside of that? transaction_scope: read message from servicebus - UpdateCustomerAddress get customer aggregate from docdb, replay events where commited =1 call customer.updateAddress validates creates customer address updated event apply event event store as uncommitted events do optimistic concurrency update against docdb pushing uncommitted events (single op to ensure consistency) publish event to service bus update docdb set events just published to commited = 1 (again one 1 op - at least in mongodb) transaction_complete

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  • What is the funniest bug you've ever experienced?

    - by friol
    I remember testing a geographical data normalizer written in Java that had concurrency problems. So, when you tried to normalize a city (say "Rome") and another guy did that too (say "New york"), you would get the other guy's data normalized ("NEW YORK") instead of your query. What's the bug that mostly made you smile in your career?

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